Head mounted displays (HMDs) are used to provide a virtual scenery to a user, or to augment a real scenery with additional information or additional virtual objects or scenery. Stereoscopic images can be displayed e.g. by providing separate images to each eye of the user. In some HMD systems, a head and/or eye position and orientation of the user are tracked, and the simulated scenery displayed is adjusted in real time depending on the user's head orientation and gaze direction, to provide an illusion of the user immersed into a simulated or augmented three-dimensional scenery. Presenting such simulated or augmented scenery to a user can cause visual fatigue and nausea resulting from a limited capability of existing headsets to properly compensate for a discrepancy between eye vergence and eye focusing to accommodate a visual distance, a problem known as vergence-accommodation conflict. The vergence-accommodation conflict appears as a result of changing vergence of eyes of a user depending on what virtual object the user is looking at, while the accommodation of the eyes is generally fixed and set by the distances between electronic display generating virtual images and a lens system projecting the images into user's eyes.